1. Field of the Invention
The present invention is directed to a primary radiation diaphragm for an x-ray tube of the type having two sets of diaphragm plates disposed parallel to each other, with one set being proximate the focus of the x-ray tube and the other set being distal of the focus, so that a ray pyramid is formed by adjusting the respective sets of plates.
2. Description of the Prior Art
A primary radiation diaphragm for an x-ray tube is disclosed in German OS 1 441 312 wherein a first group of diaphragm plates is formed by two diaphragm plate pairs disposed relative to each other to form an opening for the passage of radiation proximate the focus of the x-ray tube. A second group of two diaphragm plate pairs is disposed distal of the focus and parallel to the plates in the first group, the plate pairs in the second group also forming an opening for radiation passage. The diaphragm plates in each diaphragm plate pair are adjustable in common with reference to the longitudinal axis of the overall radiation diaphragm structure. The diaphragm plate pairs in the first group and the diaphragm plate pairs in the second group are symmetrically disposed relative to the longitudinal axis with the same orientation, so that a ray pyramid having a desired size is formed, the tip of the pyramid being coincident with the x-ray tube focus.
In this known structure, setting or adjustment of the diaphragm plates is undertaken by means of drive rollers and drive belts, so that the two plates in each plate pair are adjusted in common. The use of such drive rollers and drive belts makes the structure of this known primary radiation diaphragm relatively complicated. As a result of the use of a belt drive, moreover, a certain amount of play can arise upon the displacement of the diaphragm plates, which degrades the precision with which the overall radiation diaphragm structure can be set.
Another primary radiation diaphragm of the type having diaphragm plates arranged in parallel, spaced planes is commercially available under the designation "Rurek X-ray Collimator." This type of diaphragm is a so-called multi-leaf collimator with the diaphragm plates in one of the planes being arranged to form an iris diaphragm. The adjustment of the diaphragm plates in the respective diaphragm planes is undertaken separately.